Just got my lower registered as an AOW. :>

Now I need to decide what caliber to make the upper...

The muzzle velocity of .223/5.56 out of a 7.5 inch barrel is about 2100fps.  That is barely enough to stabilize it for 20 feet or so.

And, not enough to cause the hyper-velocity "magic bullet" properties of the flipping and flying apart 5.56 to come out.

Maybe I should build my encounter weapon as a 7.62 x 49mm?  May be more effective at the lower velocities cuz of the short barrel.

Any input?